Objective <p>Using structural cranial magnetic resonance imaging (MRI), we constructed a structural Brain Aging Index (sBAI) and evaluated the brain aging status, expressed as Brain Predicted Age Difference (Brain-PAD), in acute ischemic stroke patients. We aim to investigate its associations with baseline clinical and imaging characteristics, small vessel disease (SVD) burden, and 12-month functional and cognitive outcomes, and explored its potential contribution to prognostic models.</p> Methods <p>A retrospective cohort of 150 patients with acute ischemic stroke admitted between November 2021 and November 2023 was analyzed. Diffusion-weighted imaging (DWI) infarct volume, white matter hyperintensity (WMH) volume, lacunes, cerebral microbleeds (CMBs), enlarged perivascular spaces (EPVS), hippocampal volume, and cortical thickness were collected. Clinical and imaging differences were compared between the “age-matched group” (Brain-PAD &lt; + 5 years) and the “accelerated brain aging group” (Brain-PAD ≥ + 5 years).</p> Results <p>Patients in the accelerated brain aging group had significantly higher admission National Institutes of Health Stroke Scale (NIHSS) scores, larger DWI infarct volumes, greater WMH burden, and higher total SVD scores. During follow-up, the accelerated brain aging group had a lower rate of favorable functional outcome at discharge and a higher incidence of poor 12-month functional outcome, together with significantly lower MoCA scores. Admission NIHSS and WMH volume (aOR = 1.10) were independent predictors of 12-month functional outcome. sBAI was significantly associated with 12-month MoCA scores.</p> Conclusion <p>Brain aging status derived from structural MRI is closely associated with acute lesion burden, cumulative small vessel disease, and poststroke cognitive and functional outcomes.</p>